Getting the 'threaded GL dispatch' code into Mesa is causing some issues, Valve might use a white-list

You may remember recently I wrote about 'threaded GL dispatch' in Mesa possibly getting merged, after AMD's Marek suggested it and there was some backlash, well, it has continued.

For those that don't know, threaded GL dispatch will help to split up the application and OpenGL into different threads to hopefully improve performance. It can improve some games, while make things worse on others (some already do it in-engine).

Ian Romanick replied to the mailing list entry without pulling any punches:

QuoteNo, it absolutely is not fine to merge. We have never allowed such a thing, and I'll be damned if I'll allow this project to start. Things that land that are known to be broken never actually get fixed. Then we have to waste time fielding bug reports and Phoronix threads because
users turn on the performance features and everything breaks. It's just a terrible idea.

However, Eric Anholt was keen to point out they often merge-in code that's not even close to being done:

QuoteYeah, just like how we gated the GLSL compiler until it was completely done (we didn't) and NIR until it was completely done (we didn't) and Vulkan until it was completely done (we didn't) and...

Software that people care about gets fixed. I'm also concerned that nobody actually cares about getting glthread working completely, given Marek's attitude toward piglit conformance (and my also ignoring the branch for the last however many years). However, "we have never allowed merging broken software that's only turned on under env vars/configure" is totally false. We do that regularly for big things we care about.

There seems to be a lot of words being thrown around, which is perfectly normal for big changes to projects like this it's just that this is all on a public mailing list where anyone can subscribe to see it.

Also, it seems Civilization VI is another game that would benefit from it and Valve are apparently looking to use the code with a white-list on SteamOS, from Marek's post:

QuoteFYI. Civilization VI is another game that works with and benefits from glthread. The game was just released. Even Nvidia is CPU-bound on highest details and can't reach 45 fps with full hd. People wanting to play Civ VI with decent frame rate will want glthread. I don't think they care too much about our the community processes, so I expect there will be quite a few users using out-of-tree builds of Mesa.

Also, Pierre-Loup from Valve said on IRC yesterday that they are probably gonna ship glthread and make their own whitelist, regardless of the outcome of this discussion. It would be preferable to have that whitelist in master too, but that may be difficult if we can't merge it.

If distributions and vendors start shipping glthread, we might as well merge it, because at that point there is no advantage in keeping this out of tree if it forces users to use out of tree builds. We'll get bug reports regardless.

It will be very interesting to see what the real outcome is, hopefully whatever is better for the end-user and not what the developers feel should be the way because of ideological reasons or whatever. Article taken from GamingOnLinux.com.